Three-way switch systems for use in controlling loads in buildings, such as lighting loads, have long been known in the art. The switches used in these systems are wired to the building's alternating-current (AC) wiring system, are subjected to AC source voltage, and carry full load current, as opposed to low-voltage switch systems that operate at low voltage and low current and communicate digital commands (usually low-voltage logic levels) to a remote controller that controls the level of AC power delivered to the load in response to the commands. Thus, as used herein, the terms “three-way switch” and “three-way system” mean such switches and systems that are subjected to the AC source voltage and carry the full load current.
In a three-way switch system, there are two three-way switches for controlling a single load, and each switch is fully operable to independently control the load irrespective of the status of the other switch. In such a system, one three-way switch must be wired at the AC source side of the system (sometimes called “line side”), and the other three-way switch must be wired at the load side of the system.
FIG. 1A shows a standard three-way switch system 100, which includes two three-way switches 102, 104. The switches 102, 104 are connected between an AC power source 106 and a lighting load 108. When switches 102, 104 are both in position A (or both in position B), the circuit is complete and the lighting load 108 is energized. When switch 102 is in position A and switch 104 is in position B (or vise versa), the circuit is not complete and the lighting load 108 does not light up.
Three-way dimmer switches that replace three-way switches are well known in the art. An example of a three-way dimmer switch system 150 including one prior art three-way dimmer switch 152 and one three-way switch 104 is shown in FIG. 1B. The three-way dimmer switch 152 simply includes a dimmer circuit 152A and a three-way switch 152B. A typical, AC, phase-control dimmer 152 regulates the amount of energy supplied to the lighting load 108 by conducting for some portion of each half-cycle of the AC waveform, and not conducting for the remainder of the half-cycle. Because the dimmer switch 152 is in series with the lighting load 108, the longer the dimmer 152 conducts, the more energy will be delivered to the lighting load 108. Where the lighting load 108 is a lamp, the more energy delivered to the lighting load 108, the greater the light intensity level of the lamp. In a typical dimming scenario, a user may adjust a control to set the light intensity level of the lamp to a desired light intensity level. The portion of each half-cycle for which the dimmer conducts is based on the selected light intensity level. Since two dimmer circuits cannot be wired in series, the three-way dimmer switch system 150 can only include one three-way dimmer switch 152, which can be located on either the line side or the load side of the system.
Three-way dimming systems that employ a “smart” dimmer switch and a specially designed auxiliary (remote) switch that permits the dimming level to be adjusted from multiple locations have been developed. A smart dimmer is one that includes a microcontroller or other processing means for allowing an advanced set of control features and feedback options to the end user. To power the microcontroller, smart dimmers include power supplies, which draw a small amount of leakage current through the lighting load each half-cycle when the FETs are non-conducting. The power supply uses this small amount of current to charge a capacitor and develop a direct-current (DC) voltage to power the microcontroller. An example of a multiple location lighting control system, including a wall mountable smart dimmer switch and wall mountable remote switches for wiring at all locations of a multiple location switch system is disclosed in commonly assigned U.S. Pat. No. 5,248,919, issued on Sep. 28, 1993, entitled “Lighting Control Device”, which is herein incorporated by reference in its entirety.
Referring to the system 150 of FIG. 1B, since no load current flows through the dimmer circuit 152A of the three-way dimmer switch 152 when the circuit between the supply 106 and the lighting load 108 is broken by either three-way switch 152B or 104, the dimmer switch 152 is not able to include a power supply and a microcontroller. Thus, the dimmer switch 152 is not able to provide the advanced set of features of a smart dimmer to the end user.
FIG. 2 shows an example multiple location lighting control system 200 including one wall mountable smart dimmer switch 202 and one wall mountable remote, or accessory, switch 204. The dimmer switch 202 has a Hot (H) terminal, for receipt of an AC source voltage provided by an AC power supply 206, and a Dimmed Hot (DH) terminal, for providing a dimmed-hot voltage to a lighting load 208. The remote switch 204 is connected in series with the DH terminal of the dimmer switch 202 and the lighting load 208 and simply passes the dimmed-hot voltage through to the lighting load.
The dimmer switch 202 and the remote switch 204 both have actuators to allow for raising, lowering, and toggling on/off the lighting load 208. The dimmer switch 202 is responsive to actuation of any of these actuators to alter the dimming level (or power the lighting load 208 on/off) accordingly. In particular, actuation of an actuator at the remote switch 204 causes an AC control signal, or partially rectified AC control signal, to be communicated from that remote switch 204 to the dimmer switch 202 over the wiring between the Accessory Dimmer (AD) terminal of the remote switch 204 and the AD terminal of the dimmer switch 202. The dimmer switch 202 is responsive to receipt of the control signal to alter the dimming level or toggle the load on/off. Thus, the load can be fully controlled from the remote switch 204.
The user interface of the dimmer switch 202 of the multiple location lighting control system 200 is shown in FIG. 3. As shown, the dimmer switch 202 may include a faceplate 310, a bezel 312, an intensity selection actuator 314 for selecting a desired level of light intensity of a lighting load 208 controlled by the dimmer switch 202, and a control switch actuator 316. Faceplate 310 need not be limited to any specific form, and is preferably of a type adapted to be mounted to a conventional wall box commonly used in the installation of lighting control devices. Likewise, bezel 312 and actuators 314 and 316 are not limited to any specific form, and may be of any suitable design that permits manual actuation by a user.
Actuation of the upper portion 314A of actuator 314 increases or raises the light intensity of lighting load 208, while actuation of lower portion 314B of actuator 314 decreases or lowers the light intensity. Actuator 314 may control a rocker switch, two separate push switches, or the like. Actuator 316 may control a push switch, though actuator 316 may be a touch-sensitive membrane or any other suitable type of actuator. Actuators 314 and 316 may be linked to the corresponding switches in any convenient manner. The switches controlled by actuators 314 and 316 may be directly wired into the control circuitry to be described below, or may be linked by an extended wired link, infrared link, radio frequency link, power line carrier link, or otherwise to the control circuitry.
Dimmer switch 202 may also include an intensity level indicator in the form of a plurality of light sources 318, such as light-emitting diodes (LEDs). Light sources 318 may be arranged in an array (such as a linear array as shown) representative of a range of light intensity levels of the lighting load being controlled. The intensity levels of the lighting load may range from a minimum intensity level, which is preferably the lowest visible intensity, but which may be zero, or “full off,” to a maximum intensity level, which is typically “full on.” Light intensity level is typically expressed as a percent of full intensity. Thus, when the lighting load is on, light intensity level may range from 1% to 100%.
A simplified block diagram of the dimmer switch 202 and the remote switch 204 of the multiple location lighting control system 200 is shown in FIG. 4A. The dimmer switch 202 employs a controllably conductive device, such as two field-effect transistors (FETs) 420, 422 provided in anti-serial connection between the Hot terminal H and the Dimmed Hot terminal DH, to control the current through, and thus the intensity of, the lighting load 208. The first FET 420 conducts during the positive half-cycle of AC waveform and the second FET 422 conducts during the negative half-cycle of the AC waveform. The gates of FETs 420, 422 are connected to a gate drive circuit 424, which provides control inputs to the FETs in response to command signals from a microcontroller 426. Alternatively, the controllably conductive device could be implemented as another type of semiconductor switch, such as a triac or a silicon-controlled rectifier (SCR).
Microcontroller 426 may be any suitable processing device, such as a programmable logic device (PLD), a microprocessor, or an application specific integrated circuit (ASIC). Microcontroller 426 generates command signals to a plurality of LEDs 418 for feedback to the user of the dimmer switch 202. The microcontroller 426 receives inputs from a zero-crossing detector 430 and a signal detector 432.
A power supply 428 generates two DC output voltages VCC1 and VCC2. The first output voltage VCC1 has a magnitude appropriate to power the microcontroller 426 and other low-voltage circuitry (such as 3.3 VDC or 5 VDC). The second output voltage VCC2 has a magnitude greater than VCC1 (approximately 8 VDC) and is provided to the gate drive circuit 424 for driving the FETs 420A, 420B.
The zero-crossing detector 430 determines the zero-crossing points of the input 120V, 60 Hz AC waveform from the AC power supply 206. The zero-crossing information is provided as an input to microcontroller 426. Microcontroller 426 provides the gate control signals to operate FETs 420, 422 to provide voltage from the AC power supply 206 to the lighting load 208 at predetermined times relative to the zero-crossing points of the AC waveform.
Generally, two techniques are used for controlling the power supplied to the lighting load 208: forward phase control dimming and reverse phase control dimming. In forward phase control dimming, the FETs 420, 422 are turned on at some point within each AC line voltage half-cycle and remains on until the next voltage zero-crossing. Forward phase control dimming is often used to control energy to a resistive or inductive load, which may include, for example, a magnetic low-voltage transformer or an incandescent lamp. In reverse phase control dimming, the FETs 420, 422 are turned on at the zero-crossing of the AC line voltage and turned off at some point within each half-cycle of the AC line voltage. Reverse phase control is often used to control energy to a capacitive load, which may include, for example, an electronic low-voltage transformer.
Signal detector 432 has an input 440 for receiving switch closure signals from momentary switches designated T, R, and L. Switch T corresponds to a toggle switch controlled by switch actuator 316, and switches R and L correspond to the raise and lower switches controlled by the upper portion 314A and lower portion 314B, respectively, of intensity selection actuator 314.
Closure of switch T will connect the input of the signal detector 432 to the DH terminal of the dimmer switch 202 when the FETs 420, 422 are non-conducting, and will allow both positive and negative half-cycles of the AC current to flow through the signal detector. Closure of switches R and L will also connect the input of the signal detector 432 to the DH terminal when the FETs 420, 422 are non-conducting. However, when switch R is closed, current can only flow through the signal detector 432 during the negative half-cycle of the AC power supply 406 because of a diode 434. In similar manner, when switch L is closed, current can only flow through the signal detector 432 during the positive half-cycles because of a diode 436. The duration of switch closures of switches T, R, and L are typically 100-200 milliseconds in length. The signal detector 432 detects when the switches T, R, and L are closed, and provides two separate output signals representative of the state of the switches as inputs to the microcontroller 426. A signal on the first output of the signal detector 432 indicates a closure of switch R and a signal on the second output indicates a closure of switch L. Simultaneous signals on both outputs represent a closure of switch T. The microcontroller 426 determines the duration of closure in response to inputs from the signal detector 432.
The remote switch 204 provides a means for controlling the dimmer switch 202 from a remote location in a separate wall box. The remote switch 204 includes a further set of momentary switches T′, R′, and L′ and diodes 434′ and 436′. A wire connection is made between the AD terminal of the remote switch 204 and the AD terminal of the dimmer switch 202 to allow for the communication of actuator presses at the remote switch. The AD terminal is connected to the input 440 of the signal detector 432. The action of switches T′, R′, and L′ in the remote switch 204 corresponds to the action of switches T, R, and L in the dimmer switch 202.
A schematic representation of the signal detector 432 is shown in FIG. 4B. The input 440 if the signal detector 432 is received from the switches T, R, and L and the AD terminal. Two outputs 442 (AD_LOWER) and 444 (AD_RAISE) are provided to the microprocessor 426. When the lower switch L is pressed, current will flow out of the input 440 through a diode D1 and two resistors R1, R2 of the signal detector 432 during the positive half-cycles of the AC power supply 406. When the current flows, a bias voltage will develop across the resistor R2, which will cause a transistor Q1 to begin conducting, thus pulling the output AD_LOWER up to the level of the voltage VCC2. A resistor R3 pulls the voltage at the output AD_LOWER down to circuit common during the negative half-cycles. Thus, an active-high control signal that consists of a pulse during each positive half-cycle will be generated at the output AD_LOWER when the switch L is pressed.
When the raise switch R is pressed and the breakdown voltage of a zener diode Z1 is exceeded, current will flow into the input 440 through a diode D2, the zener diode Z1, and two resistors R4, R5 during the negative half-cycles. The zener diode Z1 limits the voltage across the resistors R4, R5 and thus the current through the resistors. A bias voltage produced across resistor R5 when current flows will cause a transistor Q2 to begin conducting and the output AD_RAISE will then be pulled down to circuit common. A resistor R6 is provided to pull the voltage at the output AD_RAISE up to the voltage VCC1 during the positive half-cycles. In this case, an active-low control signal that consists of a pulse during each negative half-cycle will be generated at the output AD_RAISE when the switch R is pressed.
When the toggle switch T is pressed,current will flow through the signal detector 632 during both half-cycles and both of the control signals as described above will be generated at the outputs AD_LOWER and AD_RAISE.
When the switches T′, R′, and L′ are pressed on the remote switch 204, the signal detector 432 functions the same as when the switches T, R, and L are pressed. Also, the signal detector 432 will function similarly if the remote switch 204 is located on the line side of the dimmer switch 202. However, when switch L′ is pressed in this case, the diode D1 will conduct during the negative half-cycles and the signal at the AD_LOWER output will have pulses during the negative half-cycles. Further, when the switch R′ is pressed, the diode D2 will conduct during the positive half-cycles and the signal at the AD_RAISE output will have pulses during the positive half-cycles.
Even though the multiple location lighting control system 200 allows for the use of a smart dimmer switch in a three-way system, it is necessary for the customer to purchase the remote switch 204 along with the smart dimmer switch 202. Often, the typical customer is unaware that a remote switch is required when buying a smart dimmer switch for a three-way system until after the time of purchase when the smart dimmer switch is installed and it is discovered that the smart dimmer will not work properly with the existing three-way switch. Therefore, there exists a need for a smart three-way dimmer switch that may be installed in a three-way system without the need to purchase and install a special remote switch.